Method and system for small cell discovery in heterogeneous cellular networks

ABSTRACT

A method and a user equipment in a network having a macro cell and at least one small cell, the method in one embodiment receiving a measurement restriction over a broadcast channel from the macro cell; and applying the restriction for a corresponding measurement at the user equipment. In one embodiment the method includes receiving a small cell list from the macro cell; and measuring at least one of a reference signal receive power and a reference signal received quality based on the received small cell list. The method includes, in one embodiment, receiving a neighboring small cell configurations from the macro cell; and utilizing the received small cell configurations to attach to a small cell. The method includes, in one embodiment, receiving an s-measure offset value over a broadcast channel from the macro cell; and applying the s-measure offset value to an s-measure for neighbor cell discovery.

RELATED APPLICATIONS

The present application is a non-provisional of U.S. ProvisionalApplication No. 61/539,333, filed Sep. 26, 2011, the entire contents ofwhich are incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to heterogeneous networks and inparticularly relates to networks having small cells within a macro cell.

BACKGROUND

Various mobile architectures include a macro cell having smaller cellsfound within these macro cells. One example is the long-term evolutionadvanced (LTE-A) communication standard in which a user equipment (UE)may communicate with both the macro cell and small cells, such as picocells or femto cells or relay cells. The use of LTE-A is however notlimiting any other similar networks are possible.

In a LTE-A heterogeneous network, pico cells could be deployed withoverlaid macro cells. The pico cells could share the same carrier withthe macro cell or use different carriers.

In order to connect to a small cell, a UE needs to find the small cellto connect to. This is typically done by scanning for a reference signalfor the small cell. However, UE power consumption may be affected by thesearch for pico cells, especially when the pico cells use a carrierfrequency different from that of the macro cells.

Further, delays in transitioning to an available small cell due to thesearching process could degrade a user's experience. In particular, topreserve battery life a UE may only periodically search for other cellsincluding pico cells. Thus, the transition to a small cell may bedelayed, leading to sub-optimal data throughput for the device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be better understood with reference to thedrawings, in which:

FIG. 1 is a block diagram illustrating a heterogeneous network having aclosed subscriber group cell within a macro cell;

FIG. 2 is a block diagram illustrating a heterogeneous network having apico cell within a macro cell;

FIG. 3 is a block diagram showing subframe transmission at a macro layerand at a pico layer where the macro layer includes almost blanksubframes;

FIG. 4 is a block diagram illustrating communications between the macroeNB and UE and a pico eNB and UE;

FIG. 5 is a flow diagram illustrating transmission of serving andneighbor restriction patterns from an eNB to a UE;

FIG. 6 is flow diagram illustrating transmission of a small cell listfrom an eNB to a UE;

FIG. 7A is a block diagram showing transmission of subframes at a macrolayer and a pico layer in which the macro layer and pico layer are timesynchronized;

FIG. 7B is a block diagram showing transmission of subframes at a macrolayer and a pico layer in which the macro layer and pico layer are nottime synchronized;

FIG. 8 is a flow diagram illustrating transmission of a S-measure offsetvalue from an eNB to a UE;

FIG. 9 is a flow diagram illustrating transmission of a dedicatedmessage providing a small cell list from an eNB to a UE;

FIG. 10 is a flow diagram illustrating transmission of a dedicatedmessage providing a subframe offset value from an eNB to a UE;

FIG. 11 is a flow diagram illustrating transmission of a dedicatedmessage providing a small cell location from an eNB to a UE;

FIG. 12 is a flow diagram illustrating communication between an eNB anda UE for requesting and sending measurement configuration information;

FIG. 13 is a simplified block diagram of a network element capable ofbeing used with the embodiments of the present disclosure; and

FIG. 14 is a block diagram of an example mobile device.

DETAILED DESCRIPTION

The present disclosure provides a method at a user equipment in anetwork having a macro cell and at least one small cell, the methodcomprising: receiving a measurement restriction over a broadcast channelfrom the macro cell; and applying the restriction for a correspondingmeasurement at the user equipment.

The present disclosure further provides a user equipment configured tooperate in a heterogeneous network having a macro cell and at least onesmall cell, the user equipment comprising: a processor; and acommunication subsystem, wherein the processor and communicationsubsystem cooperate to: receive a measurement restriction over abroadcast channel from the macro cell; and apply the restriction for acorresponding measurement at the user equipment.

The present disclosure further provides a method at a user equipment ina network having a macro cell and at least one small cell, the methodcomprising: receiving a small cell list from the macro cell; andmeasuring at least one of a reference signal receive power and areference signal received quality based on the received small cell list.

The present disclosure further provides a user equipment configured tooperate in a heterogeneous network having a macro cell and at least onesmall cell, the user equipment comprising: a processor; and acommunication subsystem, wherein the processor and communicationsubsystem cooperate to: receive a small cell list from the macro cell;and measure at least one of a reference signal receive power and areference signal received quality based on the received small cell list.

The present disclosure further provides a method at a user equipment ina network having a macro cell and at least one small cell, the methodcomprising: receiving a neighboring small cell configurations from themacro cell; and utilizing the received small cell configurations toattach to a small cell.

The present disclosure further provides a user equipment configured tooperate in a heterogeneous network having a macro cell and at least onesmall cell, the user equipment comprising: a processor; and acommunication subsystem, wherein the processor and communicationsubsystem cooperate to: receive a neighboring small cell configurationsfrom the macro cell; and utilize the received small cell configurationsto attach to a small cell.

The present disclosure further provides a method at a user equipment ina network having a macro cell and at least one small cell, the methodcomprising: receiving an s-measure offset value over a broadcast channelfrom the macro cell; and applying the s-measure offset value to ans-measure for neighbor cell discovery.

The present disclosure further provides a user equipment configured tooperate in a heterogeneous network having a macro cell and at least onesmall cell, the user equipment comprising: a processor; and acommunication subsystem, wherein the processor and communicationsubsystem cooperate to: receive an s-measure offset value over abroadcast channel from the macro cell; and apply the s-measure offsetvalue to an s-measure for neighbor cell discovery.

The present disclosure further provides a method at a user equipment ina network having a macro cell and at least one small cell, the methodcomprising: receiving an indication over a dedicated connection from themacro cell to activate or deactivate small cell measurements; andactivating or deactivating the small cell measurements based on theindication.

The present disclosure further provides a user equipment configured tooperate in a heterogeneous network having a macro cell and at least onesmall cell, the user equipment comprising: a processor; and acommunication subsystem, wherein the processor and communicationsubsystem cooperate to: receive an indication over a dedicatedconnection from the macro cell to activate or deactivate small cellmeasurements; and activate or deactivate the small cell measurementsbased on the indication.

A heterogeneous network is a network which is designed to provide abalance of coverage needs and capacity. It may include macro cells andlow-power nodes such as pico cells, femto cells, and relays, amongothers. The macro cells overlay the low-power nodes or small cells,sharing the same frequency or on different frequencies. In oneembodiment, small cells are utilized to offload capacity from macrocells, improve indoor and cell edge performance, among other factors.For example, near a cell edge, a mobile device that connects to a picocell may have better data throughput than when connecting to the macrocell.

In heterogeneous network deployment, inter-cell interferencecoordination (ICIC) plays an important role and time domain basedresource sharing or coordination has been provided as an enhanced ICIC(eICIC). The eICIC is also known as the Almost Blank Subframe (ABS)based solutions. In such an ABS based solution, a dominant cell willtransmit almost no information in a certain subframes.

There are two main deployment scenarios where eICIC is utilized. Theseinclude the closed subscriber group (femto cell) scenario and the picocell scenario.

Reference is now made to FIG. 1, which shows the closed subscriber groupscenario. In FIG. 1, macro evolved Node B (eNB) 110 has a cell coveragearea shown by circle 112.

Similarly, closed subscriber group (CSG) cell 120 has a coverage areashown by circle 122.

A non-member UE 130 enters into the CSG coverage area 122. However,since UE 130 is not a member of CSG cell 120, UE 130 cannot connect toCSG cell 120 must continue to be served by macro cell 110. In this case,the CSG cell is dominant and has a stronger signal power than that ofmacro cell 110 and the signals from CSG cell 120 are seen asinterference at UE 130.

That is, according to FIG. 1, dominant interference conditions mayhappen when non-member users are in close proximity of a CSG cell 120.Typically, the Physical Downlink Control Channel (PDCCH) reception atthe non-member UE is interfered with by the downlink transmission fromthe CSG cell 120 to its member UEs. Interference to the PDCCH receptionof the macro cell UE 130 has a detrimental impact on both the uplink anddownlink data transfer between the UE and the macro eNB 110. Inaddition, other downlink control channels and reference signals fromboth the macro eNB 110 and neighbor cells that may be used for cellmeasurements and radio link monitoring are also interfered with by thedownlink transmission from the CSG cell 120 to its member UEs.

Depending on network deployment and strategy, it may not be possible todivert the users suffering from inter-cell interference to anotherE-UTRA carrier or other radio access technology (RAT). In this case,time domain ICIC may be used to allow such non-member UEs to remainserved by the macro cell on the same frequency layer. Such interferencemay be mitigated by the CSG cell utilizing Almost Blank Subframes (ABS)to protect the protected resources for radio resource measurement (RRM),radio link monitoring (RLM) and Channel State Information (CSI)measurements for the serving macro eNB 110, allowing the UE to continueto be served by the macro eNB under otherwise strong interference fromthe CSG cell.

Similarly, for a pico scenario, reference is made to FIG. 2. In FIG. 2,macro eNB 210 has a cell coverage area shown by circle 212. Similarly, apico cell 220 has a coverage area shown by circle 222. Pico cell 220 mayfurther include a range expansion area 232 used for increasing thecoverage area for pico cell 220.

A UE 240 is served by pico cell 220, but it is close to the edge of thepico cell coverage or in range expansion area 232 of the pico cell 220.In this case, macro eNB 210 may generate/cause significant interferencefor the UE 240.

In particular, the time domain ICIC may be utilized for a pico cell 220,for users who are served in the edge of the serving pico cell. Thisscenario may be used, for example, for traffic offloading from a macroeNB 210 to the pico cell 220. Typically, the Physical Downlink ControlChannel transmitted by the pico cell is interfered by the downlinktransmission from the macro cell. In addition, other downlink controlchannels and reference signals, from both the pico cell 220 and fromneighbor pico cells, that may be used for cell measurements and radiolink monitoring are also interfered with by the downlink transmissionfrom the macro cell.

Time domain ICIC may be utilized to allow such UEs to remain served bythe pico cell 220 at an extended range on the same frequency layer. Suchinterference may be mitigated by the macro cell using an ABS to protectthe corresponding pico cell's subframes from the interference. A UE 240served by a pico cell 220 uses the protected resources during the macrocell ABS for RRM, RLM and CSI measurements for the serving pico cell andpossible for neighboring pico cells.

In both the FIG. 1 and FIG. 2 scenarios, for the ICIC, subframeutilization across different cells are coordinated in time throughbackhaul signaling or operations, administration and maintenance (OAM)to configuration of the Almost Blank Subframe patterns. The Almost BlankSubframes in an aggressor cell are used to protect resources insubframes in the victim cell receiving strong inter-cell interferencefrom the aggressor cell.

Almost Blank Subframes are subframes with reduced transmit power andhaving no activity or reduced activity on some physical channels.However, in order to support backward compatibility for UEs, the eNB maystill transmit some required physical channels in an ABS, includingcontrol channels and physical signals as well as System Information.

Patterns based on ABSs are signaled to the UE to restrict the UEmeasurement to specific subframes called time domain measurementresource restrictions. There are different patterns depending on thetype of measured cell and measurement types.

An example of the ABS for pico scenario is shown with regards to FIG. 3.In FIG. 3, the macro layer 310 is the aggressive cell and pico layer 320is the cell that has been interfered with. As seen in the example ofFIG. 3, pico layer 320 transmits subframes with normal transmissions330, as does macro layer 310. However, macro layer 310 also includesAlmost Blank Subframes 340. Pico layer 320 may, when macro layer 310 istransmitting normal frames, schedule only UEs close to the pico cellduring these subframes. However, during the Almost Blank Subframestransmissions, the pico layer 320 may transmit to UEs close to the celledge or in the range expansion area.

Thus, in the example of FIG. 3, the macro eNB configures and transfersthe ABS patterns to pico eNB, the macro eNB does not schedule datatransmissions in ABS subframes to protect the UEs served by the pico eNBat the edge of the pico cell. The pico eNB may schedule transmission toand from the UEs in the cell center regardless of the ABS patternsbecause the macro interference is sufficiently low. During the ABSsubframes, the pico eNB 320 may schedule transmission to and from theUEs at the edge of the cell.

UEs are generally transitioned to pico or small cells in order tooffload traffic from the macro cell and to improve performance to theUE. However, in heterogeneous networks, there are currently no efficientdiscovery mechanisms for pico cells or small cells specified. As aresult, public pico cell discovery requires an exhaustive search. Evenwhen there are pico cells in a macro cell, the pico cells are normallydeployed only in some spots. Further, not all the macro cells may havepico cells. Thus, when doing an exhaustive search, the UE mustcontinuously search for pico cells throughout all frequencies, and thisresults in a considerable drain on the battery life of the UE.

When the UE is in an idle mode, the UE may need to discover the smallcells efficiently for camping purposes. In this scenario, no dedicatedconnection is established and the UE may only rely on broadcastsignaling for small cell discovery. In accordance with one embodiment ofthe present disclosure, the broadcast signaling may include informationfor such discovery.

When the UE is in the connected mode, the UE could rely on the dedicatedmeasurement configurations to optimize small cell measurements ordiscovery in accordance with one embodiment. Possible locationinformation or proximity indications could be utilized to furtherenhance the discovery procedures.

Reference is now made to FIG. 4, which shows a simplified architecturefor communication between various elements in a system. In particular, amacro eNB 410 provides cell coverage to a macro area and may server amacro UE 420, which communicates with the macro eNB 410 throughcommunication link 422.

Similarly, a pico eNB 430 communicates with a pico UE 440 through acommunication link, shown by arrow 442.

In the example of FIG. 4, pico eNB 430 is found within the area servedby macro eNB 410.

A wired or wireless backhaul link 444 is used to provide communicationand synchronization between the macro eNB 410 and pico eNB 430. Inparticular, the backhaul link 444 may be used to synchronize the ABSsubframes for macro eNB 410.

As shown in the example of FIG. 4, each element includes a protocolstack for the communications with other elements. In the case of macroeNB 410 the macro eNB includes a physical layer 450, a medium accesscontrol (MAC) layer 452, a radio link control (RLC) layer 454, a packetdata convergence protocol (PDCP) layer 456 and a radio resource control(RRC) layer 458.

Similarly, the pico eNB includes the physical layer 460, MAC layer 462,RLC layer 464, PDCP layer 466 and RRC layer 468.

In the case of macro UE 420, the macro UE includes a physical layer 470,a MAC layer 472, an RLC layer 474, a PDCP layer 476, an RRC layer 477and a non-access stratum (NAS) layer 478.

Similarly, the pico UE 440 includes the physical layer 480, the MAClayer 482, the RLC layer 484, the PDCP layer 486, the RRC layer 487 andthe NAS layer 488.

Communications between the entities, such as between macro eNB 410 andmacro UE 420, generally occur within the same protocol layer between thetwo entities. Thus, for example, communications from the RRC layer atmacro eNB 410 travels through the PDCP layer, RLC layer, MAC layer andphysical layer and gets sent over the physical layer to macro UE 420.When received at macro UE 420, the communications travel through thephysical layer, MAC layer, RLC layer, PDCP layer to the RRC level ofmacro UE 420. Such communications are generally done utilizing acommunications sub-system and a processor, as described in more detailbelow.

RRC_IDLE

In order to detect a small cell in an efficient manner, more accuratemeasurement results may be made by adopting a restricted radio resourcemanagement (RRM)/radio link management (RLM) measurements in RRC_IDLEmode. This may be done through a broadcast by an eNB, where thebroadcast indicates the measurement restriction patterns in systeminformation blocks (SIBs) to restrict the RRM/RLM measurements at theUE.

In one embodiment, a first restriction pattern is signaled forperforming RRM/RLM measurements with respect to the serving cell andsecond restriction patterns are signaled for neighboring cell RRM/RLMmeasurements. This may be done for both inter-frequency andintra-frequency. Inter-frequency indicates a frequency that is outsidethe frequency of the serving cell, while inter-frequency indicates afrequency used by the serving cell.

In the Inter-frequency case, there may be one measurement restrictionper frequency since there is no interference but the UE may avoidmeasuring during the neighbor cell ABS. When in idle mode, a UE receivesthe measurement restrictions and the UE follows such restrictions forRRM/RLM measurements of the serving cell or neighboring cells. Further,a UE may not need to measure a cell that is located some distance awayfrom the UE based on the location of the UE and location information ofthe cell.

Thus, for example, a UE that is looking for a neighboring cell may beprovided with a restriction pattern indicating that the RRM/RLMmeasurement should not be performed during the subframes indicated bythe restriction pattern of the neighboring cells. Referring to FIG. 3,the ABS subframes 340 are shown for macro layer 310 and the restrictionpattern may be that the UE does not look for the neighboring cell duringsuch ABS subframes 340 or a subset of such ABS subframes 340.

Thus, referring to FIG. 5, a serving eNB 510 communicates with an idlemode UE 512.

At various intervals serving eNB 510 will broadcast through a broadcastchannel the serving cell and neighboring cell restriction patterns, asshown by arrow 520. This broadcast will be received by the various UEswithin the cell and UE 512 will then decode the restriction patterns anduse the restriction patterns during cell measurements.

Reference is now made to Table 1 below. Table 1 shows one example of aninformation element that can be used for restriction. In particular, theinformation element is labeled as MeasSubframePattern.

TABLE 1 MeasSubframePattern information element -- ASN1STARTMeasSubframePattern-r11 ::= CHOICE { subframePatternFDD-r11 BIT STRING(SIZE (40)), subframePatternTDD-r11 CHOICE { subframeConfig1-5-r11 BITSTRING (SIZE (20)), subframeConfig0-r11 BIT STRING (SIZE (70)),subframeConfig6-r11 BIT STRING (SIZE (60)), ... }, ... } -- ASN1STOP

From the above, the information element includes various information,including the subframe pattern for frequency division duplex (FDD). Inthe example of Table 1 the subframe pattern for the FDD is a bit stringhaving forty bits.

Further, the information element of Table 1 includes a subframe patternfor time division duplex (TDD). The subframe pattern for the TDDincludes three bit strings each of varying sizes.

The subframe pattern of the information elements of Table 1 could beutilized for communicating both the serving cell and neighboring cellrestriction patterns.

The information elements may be added to various system informationblocks (SIBs), depending on whether the pattern is for the serving cell,an intra-frequency cell or an inter-frequency neighboring cell. In eachcase, the system information block could include an indication to eitherrelease the restriction pattern for the UE, or to set up a restrictionpattern for the RRM/RLM measurements.

In particular, the Third Generation Partnership Project (3GPP) TechnicalSpecification 36.331, “Radio Resource Control (RRC): ProtocolSpecification” could be modified in accordance with the informationelements shown in Appendix A. In particular, a system information blocktype 3 information element could be utilized for setting a restrictionpattern for the serving cell, a system information block type 4information element could be used for setting a restriction pattern forintra-frequency neighboring cells, and a system information block type 5information could be used for setting the restriction pattern forinter-frequency carrier neighboring cells. The examples in Appendix Aare however not limiting, and other examples of information elements orbroadcast messages are possible.

The information broadcast will generally be from an RRC layer of aserving eNB to the RRC layer of a UE. However, the messaging could alsobe on other layers.

Cell_List for Small Cells

In addition to providing restriction patterns, in one embodimentcell_lists may be provided to allow the UE to determine the searchingfor neighboring cells. In particular, it is not power efficient for theUE to monitor or search for small cells including pico cells all thetime, especially for inter-frequency cases. The UE may continuously haveto measure the reference signal receive power (RSRP) on all neighboringfrequencies for all possible cell identifiers. This could quickly draina UE's battery.

In one embodiment, the eNB may therefore provide additional informationto allow the UE to perform pico cell or small cell searching proceduresmore efficiently. In one alternative, the eNB may broadcast theidentities of pico cells within the coverage area. In this way, whenevera UE camps on a cell, it is aware of pico cells around and could performsmall cell searching procedures only for pico cells within the list.

For example, in the case of an inter-frequency search, if the UE isaware that there are no close-by pico cells on other frequencies, the UEdoes not need to start the inter-frequency pico cell searching, and thiscould save the UE's battery power.

In an intra-frequency search, if the UE is aware of the close-by smallcell_list, the UE could search for only those cells and thus reducepotential blind detections.

Thus, for both inter-frequency and intra-frequency, the UE could godirectly to measure the frequencies provided in the small cell_listinstead for using blind detection, which could drain the battery power.

In one embodiment, a system information block could include a smallcell_list, which may be a sequence of physical cell ranges. Thecell_list could include a plurality of cells depending on the number ofpico cells within the macro area.

Further, in one embodiment the cell_list could include a locationidentifier indicating the location of the pico cell. This locationidentifier could be used by the UE to further restrict the RSRPmeasurement for only those pico cells that are in close proximity to theUE. Each UE could implement its own definition of “close proximity” insome embodiments. Therefore, for example, if a UE is within 200 metersof a first pico cell but is more than 400 meters from a second picocell, the eNB may start to monitor the RSRP for the first pico cell butmay ignore the second pico cell. The distances in the above examples aremeant for illustrative purposes only and are not limiting. In someembodiments the eNB could also signal some parameters to the UE todetermine the “close proximity”, for example, within X meters of thepico cell. The value of “X” may be signaled by the eNB.

In the case that the UE cannot determine its own location, the UE maytry to measure all cells on the list. This may occur if the UE has noGPS signal or is not equipped with GPS a receiver.

The cell_list may be provided in accordance with the example of FIG. 6.In the example of FIG. 6, the UE 612 is in idle mode and camped on eNB610.

eNB 610 broadcasts system information blocks that include a smallcell_list and may also include “X”. The parameter “X” may be specifiedfor each of the small cells within the surrounding area. This is shownby arrow 620.

On receiving the broadcast with the small cell_list, UE 612 will thenmonitor the RSRP/RSRQ of the small cells in accordance with the smallcell_list. This is shown, for example, by arrow 622 in FIG. 6.

The monitoring of the RSRP/RSRQ at arrow 622 could include monitoringonly the frequencies provided in the small cell_list and could alsoinclude monitoring only those small cells that are in close proximity tothe UE, as described above.

In one embodiment, the 3GPP TS.36.331 System Information Block Type 4may be used to transmit an intra-frequency small cell_list and theSystem Information Block Type 5 may be used to transmit aninter-frequency small cell_list. Examples of such information elementsfor the system information block are shown with regard to Appendix B.The examples of Appendix B are however not limiting, and other broadcastmessages containing a small cell list are possible.

The communication of the small cell list is performed, in oneembodiment, at the RRC layer of the eNB and the UE. However, in otherembodiments other layers within the eNB and UE could be used.

Subframe Offset for Small Cells

In order to apply time domain eICIC techniques, the macro cell and picocell should be time aligned on a subframe level. Otherwise, interferenceavoidance through the ABS subframe may not be effectively implemented.

For example, reference is now made to FIGS. 7A and 7B.

In FIG. 7A, a macro layer 710 transmits normal subframes 712 and almostblank subframes 714.

A pico layer 720 is time aligned on the subframe level and thereforeincludes subframes 722 which may utilize the ABS subframe of macro layer710 effectively.

Referring to FIG. 7B, macro layer 750 includes normal subframes 752 andalmost blank subframes 754. However, pico layer 760 is not time alignedand therefore, as seen in FIG. 7B, subframe 762 overlaps with a normalsubframe and therefore is not used effectively.

Thus, in accordance with FIG. 7A, the macro cell and pico cell are timealigned on the subframe level and the pico cell could safely scheduleUEs in a range expansion area. These subframes are protected from thedominant interference from the macro cell since the macro cell mutes itstransmissions during the subframes.

However, in FIG. 7B, subframe 762 is intended to be protected from thedominant interference but partial dominant interference still existssince the subframes are not aligned. Therefore, subframe 762 cannot beused by UEs in the range expansion area for the pico cell. This is aresource waste since the macro cell intends to mute transmissions infour subframes but the pico cell can only benefit from three subframesdue to the misalignment.

Further, in FIG. 7A, the macro cell and pico cell are not necessarilyaligned at the radio frame level. In other words, there could be aninteger number of subframe offsets between the start of the radio framesfrom the macro cell and the pico cell. In the examples below, it isassumed that the macro cell and pico cell are aligned on a subframelevel but with an “n” subframe offset between the start of the radioframes. In one embodiment, n may be 0, which is a common configurationfor LTE TDD systems and also a likely configuration for LTE FDD systems.

If a UE is in the range expansion area of the pico cell, if n is 0 thenthe UE may not be able to reliably detect the primary synchronizationsequence (PSS), secondary synchronization sequence (SSS) or masterinformation block (MIB) information due to dominant interference fromthe macro cell. Even in ABS subframes, the macro cell may continue totransmit the PSS/SSS/MIB for backward compatibility purposes.

If a subframe offset is utilized between the macro cell and the picocell, then the interference on the primary synchronization sequence,secondary synchronization sequence and master information block may beavoided for UEs in the range expansion area of the pico cells. However,n=0 is a common configuration for LTE TDD systems.

In one alternatively, the network may signal a value of n to the UE aswell as the physical cell identifier (PCI). In this case, the UE may beaware that n=0 for the pico cell as well as the PCI of the pico cell.The UE could directly detect the RSRP or the reference signal receivedquality (RSRQ) of the pico cell without first detecting the primarysynchronization sequence, the secondary synchronization sequence (SSS)and the master information block (MIB).

A cell-specific reference signal (CRS) sequence is defined by:

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {2m} )}}} )} + {j\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {{2m} + 1} )}}} )}}},{m = 0},1,\ldots\mspace{14mu},{{2N_{RB}^{\max,{DL}}} - 1}} & (1)\end{matrix}$

where n_(s) is the slot number within a radio frame and l is theorthogonal frequency division multiplexing (OFDM) symbol number withinthe slot. The pseudo-random sequence generator which generates c(i) maybe initialized with c_(init)=2¹⁰·(7·(n_(s)+1)+l+1)·(2·N_(ID)^(cell))+2·N_(ID) ^(cell)+N_(CP) at the start of each OFDM symbol where:

$\begin{matrix}{N_{CP} = \{ \begin{matrix}1 & {{for}\mspace{14mu}{normal}\mspace{14mu}{CP}} \\0 & {{for}\mspace{14mu}{extended}\mspace{14mu}{CP}}\end{matrix} } & (2)\end{matrix}$

From the above, if the UE is aware that n=0, knows the PCI of the picocell and the cyclic prefix (CP) type, whether normal or extended, the UEmay derive the CRS sequence. Further, actual resource elements that areused to transmit the CRS are only dependent on the value of n and thePCI. Therefore, given n, the PCI and CP type, the UE could directlymeasure the RSRP and RSRQ of the pico cell without first detecting thePSS/SSS.

In another alternative, only the PCI and the CP type may be signaled. Inthis case, the UE could blindly detect the slot and subframe boundarysince there are only a limited number of possibilities for the CRSsequences based on the slot index and symbol index. Then the UE couldmeasure the RSRP and RSRQ without any ambiguity.

However, the UE may still need information from the MIB for campingpurposes. Since dominant interference also exists on the MIB of the picocell when n=0, this information may be required.

Currently, MIB includes the following information:

TABLE 2 MasterInformationBlock -- ASN1START MasterInformationBlock ::=SEQUENCE { dl-Bandwidth ENUMERATED { n6, n15, n25, n50, n75, n100},phich-Config PHICH-Config, systemFrameNumber BIT STRING (SIZE (8)),spare BIT STRING (SIZE (10)) } -- ASN1STOP

From Table 2 above, the master information block includes the downlinkbandwidth, the configuration information of physical hybrid automaticrepeat request (HARQ) indicator channel (PHICH) and the system framenumber (SFN).

If the UE can further be signaled with the downlink bandwidth, PHICHconfiguration and system frame number information of the surroundingpico/small cells the UE could directly measure the RSRP/RSRQ of the picocell and camp on the pico cell successfully. With this signaledinformation, done through broadcast signaling, the UE could receiveother system information block information reliably.

The system frame number information may need to be detected. Note thateven when n is 0, the SFN of the macro cell and SFN of the pico cell arenot necessarily aligned. They could be offset by “m” frames, where m isan integer from 0 to 4095. To make sure that the UE is aware of the SFNof the pico cell, m should be signaled to the UE as well in oneembodiment. In an alternative embodiment, the absolute SFN informationof small cells may be signaled to the UE.

Based on the above, for UEs in RRC_IDLE mode, to resolve the small celldiscovery issues when n is 0, the macro cell may broadcast cellidentifies of small cells, the CP type of the small cells, the downlinkbandwidth of the small cells, the PHICH configuration of the small celland the SFN offset (m) of the small cell.

In an alternative, the macro cell may broadcast for each pico cellwithin its coverage a value of n, the cell identity, the CP type and thedownlink bandwidth. If n is 0, the PHICH configuration if n is 0, andthe SFN offset if n is 0.

Note that if n is not 0, the UE could reliably detect the PSS/SSS/MIBwithout dominant interference from the macro cell. In a furtherembodiment, the downlink bandwidth, the PHICH configuration and the SFNoffsets could also be broadcast to the UE even when n does not equal 0.In this case, the UE may use the information directly without detectingthe PSS/SSS/MIB, which may save UE battery power.

Further, various information such as the CP type of the small cell, thedownlink bandwidth of the small cell, the PHICH configuration of thesmall cell may not be exchanged between the macro eNB and pico eNB overan X2 interface. Therefore, in order to enable the above, the X2interface may be used to exchange such information utilizing X2APsignaling over the X2 interface, for example. The information mayinclude the CP type of the small cell, the downlink bandwidth of thesmall cell, the PHICH configuration and the SFN off-set information.

Reference is now made to Table 3, which shows an example of informationwhich may be added to a system information block.

TABLE 3 Offest Information Intra/Inter FreqSmallCellInfo ::= SEQUENCE {physCellId PhysCellId, sf-offset BIT STRING (SIZE (4))  OPTIONAL, needOR cp-type BOOLEAN OPTIONAL, need OR dl-Bandwidth ENUMERATED { n6, n15,n25, n50, n75, n100} OPTIONAL, need OR phich-Config PHICH-Config OPTIONAL, need OR systemFrameNumber-offset BIT STRING (SIZE (12))OPTIONAL, need OR }

In the above, the information includes the physical cell ID, thesubframe offset, the cyclic prefix type, the downlink bandwidth, thePHICH configuration and the system frame number offset. However, not allof this information is required, as indicated above, and in someinstances only one of the above pieces of information may be required.In other embodiments two or more of the physical ID, the subframeoffset, the CP type, the downlink bandwidth, the PHICH configuration andthe system frame number offset may be provided in an informationelement.

If the system information blocks from 3GPP TS 36.331 are used, the aboveinformation may be provided in System Information Block Type 4 forintra-frequency small cell information and in System Information BlockType 5 for inter-frequency small cell information. Exemplary SystemInformation Block Information Elements For Both Type 4 and Type 5 areprovided in Appendix C. Such system information blocks are meant to beillustrative only and are not meant to be limiting.

Again, the offset information may be provided utilizing the RRC layer ofthe eNB and the UE in one embodiment. However, other protocol layers maybe used in other embodiments.

S-Measure Modification

The S-measure provides a threshold for determining when to scan forother cells. Thus, when a UE camps on a cell, the UE may not performintra-frequency measurements or inter-frequency measurements until thefollowing conditions are met. For intra-frequency measurements, theconditions are: Srxlev<=S_(IntraSearchP) or Squal<=S_(IntraSearchQ); forthe inter-frequency measurements, the serving cell fulfillsSrxlev<=S_(nonIntraSearchP) or Squal<=S_(nonIntraSearchQ).

The above are known as the S-measure and the parameters (e.g.,S_(IntraSearchP) S_(IntraSearchQ), S_(nonIntraSearchP),S_(nonIntraSearchQ)) are designed based on homogeneous deployments.Normally only when signal quality of the serving cell becomes bad doesthe UE starts to search for new cells on the same or differentfrequencies. This may not be efficient for heterogeneous networkdeployment. In heterogeneous networks, when the UE is in a rangeexpansion area of a pico cell, the UE may still not performintra-frequency measurements or inter-frequency measurements since thesignal quality of the serving cell is above the threshold.

For offloading purposes of pico cells, a bias may be used to startcorresponding measurements of pico cells. The bias may be included inSIB Type 4 and SIB Type 5 messages, even though the signal quality ofthe serving cell is still acceptable. The UEs could be biased to camp onthe pico cells and hence offloading off the macro cell may be achieved.

One embodiment of the present disclosure includes the addition of a newoffset value to relax the serving cell S-measurement criteria. The newoffset value for either of the intra or inter-frequency cases may beprovided in a system information block. Thus, when a UE receives the newoffset value, the UE may perform intra-frequency measurements orinter-frequency measurements until the following conditions are met. Forintra-frequency, the serving cell meets the following criteria:Srxlev<=S_(IntraSearchP)+q-small-intra-P orSqual<=S_(IntraSearchQ)+q-small-intra-Q. In some embodiments,q-small-intra-P and q-small-intra-Q may or may not be the same. If theyare the same, it could, for example, be simply represented byq-small-intra.

For inter-frequency measurements, the serving cell meets the followingcriteria: Srxlev<=S_(nonIntraSearchP)+q-small-inter-P orSqual<=S_(nonIntraSearchQ)+q-small-inter-Q. In one embodiment,q-small-inter-P and q-small-inter-Q may or may not be the same. If theyare the same, it could, for example, be simply represented byq-small-inter.

Thus, in accordance with the above, the offset is used to lower thethreshold to search for other cells.

Reference is now made to FIG. 8, which shows the signaling. Inparticular, an eNB 810 communicates through a broadcast channel with aUE 812. eNB 810 provides, in a broadcast message, the offset value, asshown by arrow 820. The UE, upon receiving the off-set value, utilizesthe off-set value to determine whether to scan for a pico cell, as shownby arrow 822.

In one embodiment, the off-set may be one of an enumerated list. Forexample, reference is now made to Table 4.

TABLE 4 s-measure offset q-small-intra / inter ENUMERATED { dB0, dB1,dB2, dB3, dB4, dB5, dB6, dB8, dB10, dB12, dB14, dB16, dB18, dB20, dB22,dB24}, OPTIONAL -- Need OP

The example of Table 4 may be applied to either the intra-frequency orinter-frequency cases and in one embodiment both intra andinter-frequency q offsets are provided in a system information block.

In one embodiment, the 3GPP TS 36.331 System Information Block Type 3may be used to broadcast the off-set value. This is shown, for example,with relation to Appendix D. The example of Appendix D is meant to beexemplary only and is only for illustrative purposes.

Again, the q offset information may be provided utilizing the RRC layerof the eNB and the UE in one embodiment. However, other protocol layersmay be used in other embodiments.

RRC CONNECTED

In an RRC_CONNECTED mode, a dedicated connection exists between a UE andan eNB. In this regard, higher level signaling could be used forcommunication between the two.

When the UE is in the RRC_CONNECTED mode, if the network is signaling apico cell list within its coverage area, this could help the UEefficiently search for the “right” pico cells to use rather thanperforming a default search of all possible pico cells, especially forinter-frequency measurements. This could, again, enhance the batterylife of the UE.

For example, in one embodiment, the UE operates in macro cell withoutany pico cells. In this case, the UE does not need to search for anypico cells on different frequencies. Thus, similar to the RRC IDLEsolutions, a small cell list may be provided to the UE.

However, since the UE is in the connected mode, the small cell listcould be provided through higher layer signaling between the UE and eNB.

Reference is now made to FIG. 9. In FIG. 9, an eNB 910 communicates withthe connected UE 912. In the embodiment of FIG. 9, a dedicated messagemay be provided to UE 912 providing the small cell list, as shown byarrow 920. The connected UE 912 can then use this small cell list, asshown by arrow 922 to scan for small cells.

In one embodiment, the small cells may be added to the 3GPP TS 36.311MeasObjectEUTRA information element (IE) sent from the eNB to the UE.The IE may be used for both the inter-frequency and intra-frequencymeasurements.

The MeasObjectEUTRA message, as defined in 3GPP TS 36.331 may bemodified in accordance with the example of Appendix E. However, AppendixE is only illustrative of one option for the modification of thismessage. Further, other messages and information elements could be usedto provide such information.

The small cell information provided in the message could be similar tothe small cell information provided above with regard to the idle modeUE.

In the further embodiment, if the eNB knows the location of the UE, theMeasObjectEUTRA information element may be customized for a particularUE by including only pico cells that are in close proximity to the UE.This would have the effect of having the UE only scan for pico cellswhen the UE is close to that pico cell. If information regarding aparticular pico cell is not contained in the small cell list provided tothe UE, the UE would not scan for such a pico cell.

In a further alternative, the MeasObjectEUTRA information element couldinclude all pico cells under the eNB domain, as well as correspondinglocation information for the pico cells. The UE may then select picocells to measure based on a comparison between the UE's own location andthe provided pico cell location information. If the UE cannot determineits own location, for example if no GPS signals are detected or if theUE does not have the GPS receiver, the UE may try to measure all picocells listed within the small cell list.

The signaling of the dedicated message between the eNB and UE may, inone embodiment, be done at the RRC layer of the protocol stack. However,the signaling may be performed at other layers in some embodiments.

Subframes Offset for Small Cells

Similar to the idle mode UE solution above, when the UE is in the RRCCONNECTED mode and the subframe offset between the macro cell and picocells is zero, the UE may have difficulty obtaining the PSS/SSS of thesmall cells due to the dominant interference from the macro cell. Evenin ABS subframes, the macro cell may continue to transmit the PSS/SSSfor backward compatibility reasons.

If a subframe offset is utilized between the macro cell and pico cell,the interference on the PSS/SSS may be avoided for UEs in the rangeexpansion area of the pico cells. However, n=0 is a common configurationfor LTE TDD systems and also a likely configuration for LTE FDD systems.

Thus, in one embodiment, if the UE can be signaled with the CP type andthe cell identity of pico cells, the UE could directly measure theRSRP/RSRQ of the pico cell without first detecting the PSS/SSS. This issimilar to the solution described above with regard to an IDLE mode UE.

Further, in the RRC_CONNECTED mode, the PHICH-config and SFN offset maynot be needed to be signaled since the macro cell may signal thisinformation to the UE in a handover command message.

The downlink bandwidth is signaled to the UE in a measurementconfiguration. Therefore, when the UE is in the RRC_CONNECTED mode, inorder to resolve the small cell discovery issues when n=0, the macrocell may signal the cell identity of the small cell and the CP type ofthe small cell through dedicated signaling. In one embodiment thesignaling may be done through measurement configurations.

In a further embodiment, the macro cell may signal, for each pico cellwithin its coverage area, the value of n, the cell identity and the CPtype (if n=0). If n˜=0, the UE could reliably detect the PSS/SSS withoutdominant interference from the macro cell.

In yet a further embodiment, the CP type could be signaled to the UEeven when n˜=0. In this case, the UE may use the information directlyfor RSRP/RSRQ measurements without detecting the PSS/SSS. This may savebattery power on the UE.

In a further alternative, only the PCI and the CP type are signaled,even when n˜=0. In this case, the UE could blindly detect the slot andthe subframe boundary since there are only a limited number ofpossibilities for the CRS sequences based on the slot index and symbolindex. The UE can then measure the RSRP/RSRQ without any ambiguity.

Reference is now made to FIG. 10. In FIG. 10, eNB 1010 communicates withUE 1012. A dedicated message, shown by arrow 1020, is used to providethe subframe offset information to the UE 1012. Such information couldinclude one or more of the physical cell identifier, the subframe offsetand the cyclic prefix type.

The UE 1012 then uses such information for small cell detection, asshown by arrow 1022.

In one embodiment, the dedicated message may be a MeasObjectEUTRAinformation element in accordance with 3GPP TS 36.331. One option formodifying this information element is showed with regard to Appendix F.However, the embodiment of Appendix F is not meant to be limiting andother options are possible.

The signaling of the dedicated message between the eNB and UE may, inone embodiment, be done at the RRC layer of the protocol stack. However,the signaling may be performed at other layers in some embodiments.

Activation/Deactivation of Small Cell Measurements

When a UE enters a macro cell, if the UE immediately startsinter-frequency pico cell searches based on the measurementconfigurations, this may not be efficient for the battery powerconsumption since the pico cells may be quite far away from the UEwithin the macro cell. Further, the coverage of the pico cell may besmall, and it may take a long time for the UE to move into the coveragearea of the pico cell.

Further, since measurement gap is utilized in the inter-frequencymeasurements, this could potentially reduce both the DL/UL datathroughput for the UE if the inter-frequency measurement is startedunnecessarily early. It is therefore more efficient for the UE to startthe measurements when the UE is close to the pico cell. One possible waythe above may be accomplished is that the network could signal locationinformation of the pico cells to the UEs. The signaling may be donethrough a dedicated message such as the MeasObjectEUTRA informationelement of 3GPP TS 36.331. However, other dedicated messaging could alsobe used.

Hence, UEs with positioning capability such as GPS could use theprovided location information for the proximity estimation to determinewhen to start monitoring for a pico cell.

Reference is now made to FIG. 11. eNB 1110 communicates with UE 1112.The eNB 1110 provides information for the pico or small cells in adedicated message, as shown by arrow 1120. The UE 1112 may then use theinformation in message 1120, along with its own GPS coordinates or otherpositioning coordinates, to determine which pico cells to look for andwhen to start the measurements, as shown by arrow 1122.

In a further alternative, a UE may request measurement configuration.When the UE detects that it is close to a pico cell, it could requestthe network to configure the measurements for the corresponding picocell measurements.

Reference is now made to FIG. 12. In the embodiment of FIG. 12, eNB 1210communicates with eUE 1212. The eUE 1212 detects as it is close to thepico cell, as shown by arrow 1220. It then sends a message, as shown byarrow 1222, to eNB 1210 to request the measurement configuration for thecorresponding pico cell measurements.

In response, eNB 1210 provides the measurement configuration, shown byarrow 1230. The UE 1212 may then use the information received in themessage of area 1230 to obtain measurements of the pico cell, as shownby arrow 1232.

In a further alternative, an adaptive measurement may be used. In thisalternative embodiment, the UE is configured with the measurements forthe pico cells initially (e.g., when the UE first enters the macrocell). However, a flag is added to the measurement configuration toindicate to the UE whether the adaptive measurement is applied.

Thus, if the flag is set to “0”, normal measurement procedures similarto Release 8, 9 or 10 of the LTE standards are applied, meaning that theUE starts the measurements immediately following measurementconfiguration.

If the flag is set to “1”, the UE does not need to start the measurementimmediately. The UE could delay the start of the correspondingmeasurements for those cells or frequencies with a flag of set to 1until the UE is close to the pico cell. The location of the pico cellmay be determined either through positioning information or automaticsearch.

In the adaptive measurement approach above, the network “grants” theright to the UE to determine when to start the measurements with thesignaled measurement configuration. In this alternative, indicators areadded into a dedicated message, such as the 3GPP TS 36.311MeasObjectEUTRA information element. The indicator could be one ormultiple bits.

If the MeasObjectEUTRA message is used, one option for such messageprovided with regard to Appendix G. However, this is not meant to belimiting and other dedicated messages could be utilized.

The above therefore provides for UE discovering small cells such as picocells efficiently in interference limited heterogeneous networkenvironments. The solutions provided above may be used individually orin conjunction with each other and may reduce the battery consumption onthe UE as well as reduce cell discovery delay.

In one embodiment, the cell list and its location information may bekept updated, through S1 or X2 interfaces.

The above may be implemented by any network element. A simplifiednetwork element is shown with regard to FIG. 13.

In FIG. 13, network element 1310 includes a processor 1320 and acommunications subsystem 1330, where the processor 1320 andcommunications subsystem 1330 cooperate to perform the methods describedabove.

Further, the above may be implemented by any UE. One exemplary device isdescribed below with regard to FIG. 14.

UE 1400 is typically a two-way wireless communication device havingvoice and data communication capabilities. UE 1400 generally has thecapability to communicate with other computer systems on the Internet.Depending on the exact functionality provided, the UE may be referred toas a data messaging device, a two-way pager, a wireless e-mail device, acellular telephone with data messaging capabilities, a wireless Internetappliance, a wireless device, a mobile device, or a data communicationdevice, as examples.

Where UE 1400 is enabled for two-way communication, it may incorporate acommunication subsystem 1411, including both a receiver 1412 and atransmitter 1414, as well as associated components such as one or moreantenna elements 1416 and 1418, local oscillators (LOs) 1413, and aprocessing module such as a digital signal processor (DSP) 1420. As willbe apparent to those skilled in the field of communications, theparticular design of the communication subsystem 1411 will be dependentupon the communication network in which the device is intended tooperate. The radio frequency front end of communication subsystem 1411can be any of the embodiments described above.

Network access requirements will also vary depending upon the type ofnetwork 1419. In some networks network access is associated with asubscriber or user of UE 1400. A UE may require a removable useridentity module (RUIM) or a subscriber identity module (SIM) card inorder to operate on a CDMA network. The SIM/RUIM interface 1444 isnormally similar to a card-slot into which a SIM/RUIM card can beinserted and ejected. The SIM/RUIM card can have memory and hold manykey configurations 1451, and other information 1453 such asidentification, and subscriber related information.

When required network registration or activation procedures have beencompleted, UE 1400 may send and receive communication signals over thenetwork 1419. As illustrated in FIG. 14, network 1419 can consist ofmultiple base stations communicating with the UE.

Signals received by antenna 1416 through communication network 1419 areinput to receiver 1412, which may perform such common receiver functionsas signal amplification, frequency down conversion, filtering, channelselection and the like. A/D conversion of a received signal allows morecomplex communication functions such as demodulation and decoding to beperformed in the DSP 1420. In a similar manner, signals to betransmitted are processed, including modulation and encoding forexample, by DSP 1420 and input to transmitter 1414 for digital to analogconversion, frequency up conversion, filtering, amplification andtransmission over the communication network 1419 via antenna 1418. DSP1420 not only processes communication signals, but also provides forreceiver and transmitter control. For example, the gains applied tocommunication signals in receiver 1412 and transmitter 1414 may beadaptively controlled through automatic gain control algorithmsimplemented in DSP 1420.

UE 1400 generally includes a processor 1438 which controls the overalloperation of the device. Communication functions, including data andvoice communications, are performed through communication subsystem1411. Processor 1438 also interacts with further device subsystems suchas the display 1422, flash memory 1424, random access memory (RAM) 1426,auxiliary input/output (I/O) subsystems 1428, serial port 1430, one ormore keyboards or keypads 1432, speaker 1434, microphone 1436, othercommunication subsystem 1440 such as a short-range communicationssubsystem and any other device subsystems generally designated as 1442.Serial port 1430 could include a USB port or other port known to thosein the art.

Some of the subsystems shown in FIG. 14 perform communication-relatedfunctions, whereas other subsystems may provide “resident” or on-devicefunctions. Notably, some subsystems, such as keyboard 1432 and display1422, for example, may be used for both communication-related functions,such as entering a text message for transmission over a communicationnetwork, and device-resident functions such as a calculator or tasklist.

Operating system software used by the processor 1438 may be stored in apersistent store such as flash memory 1424, which may instead be aread-only memory (ROM) or similar storage element (not shown). Thoseskilled in the art will appreciate that the operating system, specificdevice applications, or parts thereof, may be temporarily loaded into avolatile memory such as RAM 1426. Received communication signals mayalso be stored in RAM 1426.

As shown, flash memory 1424 can be segregated into different areas forboth computer programs 1458 and program data storage 1450, 1452, 1454and 1456. These different storage types indicate that each program canallocate a portion of flash memory 1424 for their own data storagerequirements. Processor 1438, in addition to its operating systemfunctions, may enable execution of software applications on the UE. Apredetermined set of applications that control basic operations,including at least data and voice communication applications forexample, will normally be installed on UE 1400 during manufacturing.Other applications could be installed subsequently or dynamically.

Applications and software may be stored on any computer readable storagemedium. The computer readable storage medium may be a tangible or intransitory/non-transitory medium such as optical (e.g., CD, DVD, etc.),magnetic (e.g., tape) or other memory known in the art.

One software application may be a personal information manager (PIM)application having the ability to organize and manage data itemsrelating to the user of the UE such as, but not limited to, e-mail,calendar events, voice mails, appointments, and task items. Naturally,one or more memory stores would be available on the UE to facilitatestorage of PIM data items. Such PIM application may have the ability tosend and receive data items, via the wireless network 1419. Furtherapplications may also be loaded onto the UE 1400 through the network1419, an auxiliary I/O subsystem 1428, serial port 1430, short-rangecommunications subsystem 1440 or any other suitable subsystem 1442, andinstalled by a user in the RAM 1426 or a non-volatile store (not shown)for execution by the processor 1438. Such flexibility in applicationinstallation increases the functionality of the device and may provideenhanced on-device functions, communication-related functions, or both.For example, secure communication applications may enable electroniccommerce functions and other such financial transactions to be performedusing the UE 1400.

In a data communication mode, a received signal such as a text messageor web page download will be processed by the communication subsystem1411 and input to the processor 1438, which may further process thereceived signal for output to the display 1422, or alternatively to anauxiliary I/O device 1428.

A user of UE 1400 may also compose data items such as email messages forexample, using the keyboard 1432, which may be a complete alphanumerickeyboard or telephone-type keypad, among others, in conjunction with thedisplay 1422 and possibly an auxiliary I/O device 1428. Such composeditems may then be transmitted over a communication network through thecommunication subsystem 1411.

For voice communications, overall operation of UE 1400 is similar,except that received signals would typically be output to a speaker 1434and signals for transmission would be generated by a microphone 1436.Alternative voice or audio I/O subsystems, such as a voice messagerecording subsystem, may also be implemented on UE 1400. Although voiceor audio signal output is preferably accomplished primarily through thespeaker 1434, display 1422 may also be used to provide an indication ofthe identity of a calling party, the duration of a voice call, or othervoice call related information for example.

Serial port 1430 in FIG. 14 would normally be implemented in a personaldigital assistant (PDA)-type UE for which synchronization with a user'sdesktop computer (not shown) may be desirable, but is an optional devicecomponent. Such a port 1430 would enable a user to set preferencesthrough an external device or software application and would extend thecapabilities of UE 1400 by providing for information or softwaredownloads to UE 1400 other than through a wireless communicationnetwork. The alternate download path may for example be used to load anencryption key onto the device through a direct and thus reliable andtrusted connection to thereby enable secure device communication. Aswill be appreciated by those skilled in the art, serial port 1430 canfurther be used to connect the UE to a computer to act as a modem.

Other communications subsystems 1440, such as a short-rangecommunications subsystem, is a further optional component which mayprovide for communication between UE 1400 and different systems ordevices, which need not necessarily be similar devices. For example, thesubsystem 1440 may include an infrared device and associated circuitsand components or a Bluetooth™ communication module to provide forcommunication with similarly enabled systems and devices. Subsystem 1440may further include non-cellular communications such as WiFi or WiMAX.

The embodiments described herein are examples of structures, systems ormethods having elements corresponding to elements of the techniques ofthis application. This written description may enable those skilled inthe art to make and use embodiments having alternative elements thatlikewise correspond to the elements of the techniques of thisapplication. The intended scope of the techniques of this applicationthus includes other structures, systems or methods that do not differfrom the techniques of this application as described herein, and furtherincludes other structures, systems or methods with insubstantialdifferences from the techniques of this application as described herein.

The invention claimed is:
 1. A method at a user equipment in a networkhaving a macro cell and at least one small cell, the method comprising:receiving a small cell list from the macro cell; when a signal qualitylevel of the macro cell is below a threshold, measuring signals of othermacro cells; when the signal quality level of the macro cell is belowthe threshold plus a bias, measuring at least one of a reference signalreceive power and a reference signal received quality of the small cellsin the received small cell list; and connecting to one of the smallcells from the small cell list or one of the other macro cells based onsaid measuring of the signals of the other macro cells and saidmeasuring of the reference signal receive power and the reference signalreceived quality of the small cells.
 2. The method of claim 1, whereinthe receiving is over a broadcast channel from the macro cell.
 3. Themethod of claim 2, wherein the small cell list includes at least one ofa list of small cells and frequency ranges for each of the small cellsin the list.
 4. The method of claim 3, wherein the frequency ranges areinter-frequency to the macro cell.
 5. The method of claim 4, wherein thesmall cell list is received on a Third Generation Partnership ProjectSystem Information Block Type 5 Information Element.
 6. The method ofclaim 3, wherein the frequency ranges are intra-frequency to the macrocell.
 7. The method of claim 6, wherein the small cell list is receivedon a Third Generation Partnership Project System Information Block Type4 Information Element.
 8. The method of claim 1, wherein the receivingis over a dedicated connection from the macro cell.
 9. The method ofclaim 8, wherein the small cell list is received on a Third GenerationPartnership Project MeasObjectUTRA Information Element.
 10. The methodof claim 1, wherein the small cell list further includes a location foreach small cell in the list.
 11. The method of claim 10, wherein theuser equipment only monitors small cells in close proximity to the userequipment.
 12. A user equipment configured to operate in a heterogeneousnetwork having a macro cell and at least one small cell, the userequipment comprising: a processor; and a communication subsystem,wherein the processor and communication subsystem cooperate to: receivea small cell list from the macro cell; when a signal quality level ofthe macro cell is below a threshold, measure a signal of other macrocells; when the signal quality level of the macro cell is below thethreshold plus a bias, measure at least one of a reference signalreceive power and a reference signal received quality of the small cellsin the received small cell list; and connect to one of the small cellsfrom the small cell list or one of the other macro cells based on saidmeasuring of the signals of the other macro cells and said measuring ofthe reference signal receive power and the reference signal receivedquality of the small cells.
 13. The user equipment of claim 12, whereinthe processor and communication subsystem cooperate to receive over abroadcast channel from the macro cell.
 14. The user equipment of claim13, wherein the small cell list includes at least one of a list of smallcells and frequency ranges for each of the small cells in the list. 15.The user equipment of claim 14, wherein the frequency ranges areinter-frequency to the macro cell.
 16. The user equipment of claim 15,wherein the small cell list is received on a Third GenerationPartnership Project System Information Block Type 5 Information Element.17. The user equipment of claim 14, wherein the frequency ranges areintra-frequency to the macro cell.
 18. The user equipment of claim 17,wherein the small cell list is received on a Third GenerationPartnership Project System Information Block Type 4 Information Element.19. The user equipment of claim 12, wherein the processor andcommunication subsystem cooperate to receive over a dedicated connectionfrom the macro cell.
 20. The user equipment of claim 19, wherein thesmall cell list is received on a Third Generation Partnership ProjectMeasObjectUTRA Information Element.
 21. The user equipment of claim 12,wherein the small cell list further includes a location for each smallcell in the list.
 22. The user equipment of claim 21, wherein the userequipment only monitors small cells in close proximity to the userequipment.